1. Field of the Invention
The present invention relates to a synchronous induction motor constituted by a plurality of secondary conductors provided on the peripheral portion of a rotor yoke, an end ring which is positioned on the peripheral portions of both end surfaces of the rotor yoke and which is integrally formed with the secondary conductors by die casting, and a permanent magnet embedded in the rotor yoke.
2. Description of the Related Art
Conventionally, an air conditioner or a refrigerator, for example, incorporates a hermetic electric compressor for the refrigerating cycle of a cooling unit of the air conditioner or the refrigerator. As an electric constituent for driving the compressor, an induction motor, a DC brushless motor, or a synchronous induction motor driven by a single-phase or three-phase commercial power supply has been used.
The rotor of the synchronous induction motor is constituted by a stator having stator windings and a rotor rotating in the stator. A plurality of secondary conductors positioned around a rotor yoke that makes up the rotor are die-cast. Furthermore, end rings are integrally formed with the secondary conductors by die-casting onto the peripheral portions of both end surfaces of the rotor yoke. Slots are formed through the rotor yoke, permanent magnets are inserted in the slots, and the openings at both ends of the slots are respectively secured by end surface members.
The permanent magnets to be provided in the rotor are inserted in the slots formed in the rotor yoke, then secured by fixing members. Furthermore, in order to ensure good rotational balance of the rotor, balancers are installed in the vicinity of the end rings positioned on the peripheral portions of the end surfaces of the rotor yoke. In this case, after forming the end rings by die casting, the end surface members for fixing the permanent magnets in the slots and the balancers are separately installed. This has been posing a problem in that the assembling efficiency of the synchronous induction motor is considerably deteriorated.
Furthermore, in order to secure the space for the slots for fixing the permanent magnets in the rotor, the end rings have to be made small. This inevitably leads to small sectional areas of the end rings. As a result, the heat generated by the rotor during operation increases, leading to a problem in that running performance is degraded due to degraded magnetic forces of the magnets, and, if rare earth type magnets are used for the permanent magnets, then significant demagnetization occurs.